When a specimen is analyzed with a liquid chromatograph or the like, peaks that correspond to components that are included in the analyzed specimen appear on the chromatogram. However, a peak that appears as a single shape on a chromatogram is not necessary created by a single component and may in fact represent a plurality of components that have not been sufficiently separated in a liquid chromatograph column. This has heretofore led to the use of chromatogram peak purity determination apparatus to determine whether or not a peak in a chromatogram represents a single component.
Non-Patent Literature 1 discloses peak purity determination methods that are used with chromatograms that are obtained with liquid chromatographs that use photodiode array (PDA) detectors. Using a PDA detector provides three-dimensional data consisting of wavelength, retention time and signal strength. Non-Patent Literature 1 describes two peak purity determination methods.
With the first method, the determination of the purity of a peak on a chromatogram involves comparing the absorption spectrum pattern at three points—at the peak top, peak rising slope and peak falling slope—and determining the degree of match between the spectrum pattern at the peak top and the spectrum pattern at the peak rising slope, and the degree of match between spectrum pattern at the peak top and the spectrum pattern at the peak falling slope. (The method for determining the degree of match between spectrum patterns is described in detail in Patent Literature 1.) The average value of the two degrees of match is then determined and compared against a predefined threshold value. Depending on whether or not the average value is greater than the predefined threshold value, determination is made as to whether or not there is a single peak.
With the other method, a “threshold value” and “similarity” between the absorption spectrum at the peak top and each absorption spectrum from the peak starting time to the peak ending time are calculated. The value of “similarity—threshold value” is then plotted on a time axis. Whether or not the value of “similarity—threshold value” becomes a negative value during the time that the particular peak is present is used to determine the purity of a peak (Non-Patent Literature 2).
Patent Literature 1: Examined Patent Application Publication No. 7-74761